1. Field of the Invention
The present invention relates to discharge lamps for producing luminous signs such as characters, numerals and symbols, and more particularly to plural-color discharge lamps in which the luminous color may be sequentially varied.
2. Description of the Prior Art
In general, discharge lamps may comprise a glass tube which is filled with inert gas; a pair of electrodes, one of which is mounted within the glass tub and the other is formed of a transparent conductive film deposited on the exterior surface of the glass tube; and a fluorescent film coated on the interior surface of the glass tube and adapted to produce a light in a color as desired when a discharge voltage is applied across the electrodes. One of these lamps is disclosed, for example, in Japanese Laid-Open Patent Publication No. 58-111251.
As such conventional discharge lamps have produced only a single-color light, it has been impossible for a single discharge lamp to display characters, numerals, symbols or the like in different colors changed, for example, at certain time intervals. Thus, there have been certain limitations in improving the display effect of such lamps.